Among the comfort requirements imposed on modern motor vehicles is noise and vibration damping, which includes the reduction, damping, or prevention of the introduction of vibrations which emanate, for example, from an internal combustion engine used as the power plant. For this purpose, engine mountings are designed to have specific damping properties to provide optimum damping of at least vibrations which occur at certain frequencies and amplitudes during regular engine operation. However, engine mountings designed in this manner are usually unable to damp vibrations which occur at substantially deviant frequencies and amplitudes, which may be the case, for example, when starting up and/or shutting down an internal combustion engine. Particularly great deviations from the normal operation of an internal combustion engine result when vibrations occur while starting up or shutting down internal combustion engines having direct start mechanisms, as is explained briefly below.
Different methods are used for starting up an internal combustion engine without a starter or using only minimal starter support. These methods are usually referred to as direct start or starter-supported direct start. One of these methods involves a conventional direct start using an upstream reverse rotation phase, the so-called extended direct start (described in German Patent Application No. DE 199 55 857 A1). Common to all direct start variants is the fact that the charge in the cylinders has a low air mass and a somewhat high residual exhaust gas concentration at high engine temperatures. This is additionally supported by actively closing the engine throttle valve while the internal combustion engine is coasting to avoid too strong engine vibrations, since a negative pressure ratio prevails from the exhaust valves to the intake valves during the valve overlap phase, which causes a greater amount of residual exhaust gas to flow from the exhaust manifold, for example, to the intake manifold. This process may be counteracted by using a method for the selective coasting control of an internal combustion engine, in which actively opening the throttle valve while the engine is coasting minimizes the influence of the residual exhaust gas. An electrical compressor may also be used to selectively flush the residual exhaust gas out of the cylinders with the aid of overpressure. By opening the throttle valve or flushing with the aid of overpressure, however, engine vibrations are substantially increased again by the greater piston compression during the coasting phase of the internal combustion engine. These vibrations are transmitted via conventional engine mountings to the passenger compartment, which may be unacceptable to both the manufacturer and the end customer. Even if the internal combustion engine is started up following a shutdown of the internal combustion engine controlled in this manner, e.g., in start-stop mode, using one of the aforementioned direct-start variants, the internal combustion engine begins strongly vibrating to a certain extent, since the combustion operations in the two cylinders fired first each represent a full-load combustion, in contrast to a conventional starter-controlled start, and the pistons in the internal combustion engine are greatly accelerated thereby. These vibrations are extremely pronounced, in particular in the case of extended direct start having an upstream reverse rotation phase.
Attempts have been made to weaken these vibrations, in part, by retarding the ignition angle. However, the disadvantage of this method is the fact that a required starting time is frequently unreachable thereby, since the center of mass position of the combustion operations is selectively impaired. Therefore, a conflicting goal exists between the fastest possible direct startup and a preferably low-vibration direct start, which must be taken into account when selecting the preferred direct start method.